Planctomycetes are ubiquitous bacteria with fascinating cell biological features. Strains available as axenic cultures in most cases have been isolated from aquatic environments and serve as a basis to study planctomycetal cell biology and interactions in further detail. As a contribution to the current collection of axenic cultures, here we characterise three closely related strains, Poly24^T, CA51^T and Mal33, which were isolated from the Baltic Sea, the Pacific Ocean and the Mediterranean Sea, respectively. The strains display cell biological features typical for related Planctomycetes, such as division by polar budding, presence of crateriform structures and formation of rosettes. Optimal growth was observed at temperatures of 30–33 °C and at pH 7.5, which led to maximal growth rates of 0.065–0.079 h⁻¹, corresponding to generation times of 9–11 h. The genomes of the novel isolates have a size of 7.3–7.5 Mb and a G + C content of 57.7–58.2%. Phylogenetic analyses place the strains in the family Pirellulaceae and suggest that Roseimaritima ulvae and Roseimaritima sediminicola are the current closest relatives. Analysis of five different phylogenetic markers, however, supports the delineation of the strains from members of the genus Roseimaritima and other characterised genera in the family. Supported by morphological and physiological differences, we conclude that the strains belong to the novel genus Rosistilla gen. nov. and constitute two novel species, for which we propose the names Rosistilla carotiformis sp. nov. and Rosistilla oblonga sp. nov. (the type species). The two novel species are represented by the type strains Poly24^T (= DSM 102938^T = VKM B-3434^T = LMG 31347^T = CECT 9848^T) and CA51^T (= DSM 104080^T = LMG 29702^T), respectively.

浮霉菌是普遍存在的细菌，具有令人着迷的细胞生物学特征。在大多数情况下，可用作无菌培养物的菌株已从水生环境中分离出来，并作为进一步详细研究浮霉菌细胞生物学和相互作用的基础。作为对当前无菌培养物收集的贡献，我们在这里描述了三个密切相关的菌株：Poly24 ^T 、CA51 ^T和 Mal33，它们分别从波罗的海、太平洋和地中海分离出来。这些菌株表现出相关浮霉菌的典型细胞生物学特征，例如极芽分裂、陨石坑状结构的存在和玫瑰花结的形成。在 30–33 °C 温度和 pH 7.5 下观察到最佳生长，这导致最大生长速率为 0.065–0.079 h ^-1 ，对应于 9–11 h 的世代时间。新分离株的基因组大小为 7.3–7.5 Mb，G + C 含量为 57.7–58.2%。系统发育分析将这些菌株归入Pirellulaceae科，并表明Roseimaritima ulvae和Roseimaritima sediminicola是目前最接近的亲缘关系。然而，对五种不同系统发育标记的分析支持对来自Roseimaritima属成员和该科其他特征属的菌株的描述。根据形态和生理差异的支持，我们得出结论，这些菌株属于新属Rosistilla gen。十一月并构成了两个新物种，我们建议将其命名为Rosistilla carotiformis sp。十一月和Rosistilla oblonga sp。十一月（模式种）。 这两个新物种分别由模式菌株Poly24 ^T （= DSM 102938 ^T = VKMB-3434 ^T = LMG 31347 ^T = CECT 9848 ^T ）和CA51 ^T （= DSM 104080 ^T = LMG 29702 ^T ）代表。